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    <script>
        //函数形参和实参个数匹配
        function getSum(num1, num2) {
            console.log(num1 + num2);
        }
        getSum(2, 3); //形参和实参的个数一致
        getSum(1, 2, 3); //实参的个数多于形参的个数 ,会取到形参的个数
        getSum(1);  //num2没有值，1+undefined=NaN。

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